Apparatus and method for clock phase calibration

1. An apparatus comprising:

a clock generator to generate clock signals, the clock signals being out of phase with each other;

a transmitting circuit to provide patterns of data at an output of the transmitting circuit responsive to timing of the clock signals; and

calculation and control circuitry to calculate an integral nonlinearity vector that represents offsets of transitions of the patterns from respective target positions, to generate control information based on the integral nonlinearity vector to adjust phases of the clock signals based on the control information, and to stop adjusting the phases of the clock signals responsive to the offsets of transitions from the respective target positions being within a selected range.

2. The apparatus of claim 1 , wherein the calculation and control circuitry are configured to calculate a differential nonlinearity vector based on pulse widths of unit intervals associated with the patterns of data at the output of the transmitting circuit, and the integral nonlinearity vector is calculated based on the differential nonlinearity vector.

3. The apparatus of claim 1 , wherein the clock signals include eight clock signals having eight respective phases and the control information includes eight different control codes to adjust the eight clock signals, respectively.

4. The apparatus of claim 1 , wherein the calculation and control circuitry is configured to generate the control information during a clock calibration operation.

5. The apparatus of claim 1 , wherein the calculation and control circuitry is configured to linearly adjust phases of the clock signals based on the control information.

6. The apparatus of claim 1 , wherein the patterns of data include a repeating pattern of one unit interval of a first signal level followed by a number consecutive unit intervals of a second signal level.

7. The apparatus of claim 1 , further comprising an Ethernet port coupled to the transmitting circuit.

8. The apparatus of claim 7 , wherein the transmitting circuit includes a driver including an output coupled to the output of the transmitting circuit, and an 8:1 multiplexer including an output coupled to an input of the driver.

9. An apparatus comprising:

tunable delay circuits having respective first inputs to receive respective clock signals and respective second inputs receive respective control information, the tunable delay circuits configured to adjust phases of the respective clock signals responsive to the respective control information;

a transmitting circuit including an 8:1 multiplexer to receive input data and an output to transmit output data based on timing of the clock signals, the output data having transitions based on the input data; and

calculation and control circuitry to generate an integral nonlinearity vector based on transitions of the output data at the output of the transmitting circuit, to generate the control information based on the integral nonlinearity vector, and to stop adjusting the phases of the respective clock signals responsive to offsets of the transitions of the output data from respective target positions being within a selected range.

10. The apparatus of claim 9 , wherein the input data include includes a repeating pattern of one unit interval of a first signal level followed by seven consecutive unit intervals of a second signal level.

11. The apparatus of claim 10 , wherein the first signal level is higher than the second signal level.

12. The apparatus of claim 9 , wherein the tunable delay circuits include eight tunable delay circuits, and the control information include eight different digital codes provided to respective second inputs of the tunable delay circuits.

13. The apparatus of claim 12 , wherein the eight digital codes have respective values proportional to position errors of the phases the respective clock signals.

14. A method comprising:

generating clock phases including eight different clock phases;

providing input data to a transmitting circuit;

transmitting output data at an output of the transmitting circuit based on timing of the clock phases;

calculating an integral nonlinearity vector that represents offset of transitions of the output data from respective target positions;

calculating control information based on the integral nonlinearity vector;

adjusting the clock phases based on the control information; and

stop adjusting the clock phases responsive to offsets of transitions of the output data from respective target positions being within a selected range.

15. The method of claim 12 , wherein the input data include a repeating pattern of data.

16. The method of claim 15 , wherein the repeating pattern of data includes one unit interval of a first signal level followed by a number consecutive unit intervals of a second signal level.

17. The method of claim 16 , wherein the first signal level is higher than the second signal level.

18. The method of claim 14 , wherein the output data includes a repeating pattern of data.

19. A method comprising:

generating clock phases including eight different clock phases;

providing input data to a transmitting circuit;

transmitting output data at an output of the transmitting circuit based on timing of the clock phases;

calculating an integral nonlinearity vector that represents offset of transitions of the output data from respective target positions;

calculating control information based on the integral nonlinearity vector; and

adjusting the clock phases based on the control information,

wherein:

adjusting the clock phases is performed during a clock calibration operation;

calculating the control information includes updating values of the control information in a number of cycles during the clock calibration operation; and

stopping the adjusting the clock phases responsive to the number of cycles reaches a selected number.